Scientists’ latest climate models show that the world is going to warm even more than we previously thought.
In a new study published in Geophysical Research Letters, researchers examined the sensitivity of more than two dozen new climate models. If the models are right, the goals laid out in the Paris Climate Agreement to cap global warming could be out of reach.
Climate sensitivity is one of the most important metrics in modelling. Researchers study it not by modelling real-life emissions scenarios, but instead examining how much the planet would theoretically warm if emissions doubled. On average, the new models showed Earth warming more than previous models by about 0.5 degrees Celsius. Many of the models showed that if emissions double, warming will exceed 4.5 degrees Celsius.
The researchers found that the main reason for this huge increase in warming may be due to changes cloud modelling, typically the trickiest part of climate modelling as a whole given their ephemeral nature and relatively small size in the atmosphere. Yet clouds play an important role in regulating the climate and can both cool and warm the Earth depending on the type of cloud and latitude. And global heating could affect different clouds in different ways. Mid-latitude clouds could actually change in beneficial ways.
“Middle and high latitude clouds are expected to become ‘juicier’ and hence brighter with warming, as a warmer atmosphere means more moisture is available to condense into cloud water and that ice clouds will transition to brighter liquid clouds,” Mark Zelinka, a climate expert at Lawrence Livermore National Laboratory, told Gizmodo in an email. This is good for global warming, he said, because “a brighter cloud reflects more sunlight back to space—more sunscreen.”
But Zelhenka said in new climate models, this effect isn’t as powerful in cooling the Earth as scientists once thought. At the same time, models also predict that Earth will have fewer and thinner low-level clouds, particularly in the mid-latitude Southern Hemisphere. Thick, fluffy clouds low in the atmosphere help block sunlight from Earth and protect it from some warming, so losing cloud coverage means losing that protection. There was a terrifying paper on this front last year.
“Less of them means less sunscreen,” Zelinka said.
To make matters worse, the clouds highest in the atmosphere are expected to drift even higher up. “This is a positive, amplifying feedback on global warming because it strongly limits Earth’s ability to radiate heat to space as it warms (like if your body somehow could not sweat while exercising),” Zelinka said.
The findings are troubling. But to know how much we need to worry, researchers will need to examine them further. That includes doing more experiments to see which climate models have clouds most like the ones in the real world.
“These latest highly sensitive models are very sophisticated and state-of-the-art,” said Tim Myers, a co-author of the paper, in a statement. “We take them seriously, but we also need to examine them closely to figure out if their predictions are plausible.”